【白水日记】IntentService

    IntentService继承自Service，适合处理短任务，核心实现是

ServiceHandler和Looper

private final class ServiceHandler extends Handler {

public ServiceHandler(Looper looper) {

super(looper);

}

@Override

    public void handleMessage(Message msg) {

onHandleIntent((Intent)msg.obj);

stopSelf(msg.arg1);

}

}

    ServiceHandler直接继承Handler，handleMessage只做了两件事，onHandleIntent stopSelf

@Override

public void onCreate() {

// TODO: It would be nice to have an option to hold a partial wakelock

// during processing, and to have a static startService(Context, Intent)

// method that would launch the service & hand off a wakelock.

    super.onCreate();

HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");

thread.start();

mServiceLooper = thread.getLooper();

mServiceHandler = new ServiceHandler(mServiceLooper);

}

在onCreate中，先new了一个HandlerThread，之后再通过thread的Looper,再通过looper初始化ServiceHandler 

@Override

public void onStart(@Nullable Intent intent,int startId) {

Message msg = mServiceHandler.obtainMessage();

msg.arg1 = startId;

msg.obj = intent;

mServiceHandler.sendMessage(msg);

}

在onStart中，初始化一个Message，并发送出去

@Override

public int onStartCommand(@Nullable Intent intent,int flags,int startId) {

onStart(intent,startId);

return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;

}

onStartCommand中调用onstart发送消息，执行HandleMessage中的onHandleIntent方法，之后马上stopSelf

    虽然使用起来很简单，源码也很清晰，不过在R上就会被废弃，现查看源码已经是被废弃的状态，感觉更像是一个过渡品，尤其是在Android8之后，后台执行限制导致会抛出

Caused by: java.lang.IllegalStateException: Not allowed to start service Intent: app is in background

    应用在后台几分钟之后，不能将通过startService方式进行创建后台服务，

给出的替代解决方案是WorkManager和JobIntentService方式

    JobIntentService依旧继承Service，创建工作线程处理多线程任务，线程优先级较高，不用手动结束(设计上也没有手动取消的方法)，自动关闭服务，下篇文章将详细介绍另外两种组件